Lurker, to answer your question. An examiner uses their licence number along with the rating they are using in front of it at the time. CAA guidance is that you use the correct reference for the task at that time. So as an example, I am a revalidation examiner and a Class Rating examiner. If I were to sign your licence for revalidation by experience then I would put UK/R/xxxxxxx on the ratings page with no test date just an expiration date.
If we had done an LPC instead then the ratings page would have the test date and I would sign as UK/CRE/xxxxxxx. If a PPL FE had done the LPC then he would have signed UK/FE/xxxxxxx. In practice what a lot of people are in the habit of doing is just signing with the highest authority they hold. In the case of examiner levels above R then those levels have embedded R privileges as standard. It is only in more unusual circumstances where you would have someone hold 2 separate authority's. LAA full coaches are R examiners as part of the role, but many of us have different examiner ratings to go with the day job for example so end up with 2 separate authority's.
Generally the ones you see for revalidation are:
R
FE
CRE
Each examiner is given a written authority from the CAA which contains a list of what they are authorised to do, it is a page the same size as a licence page and most people keep them with the licence. If you wish you can ask the examiner to see the authority to check if it is current and appropriate for the level you are asking them to do.
Xrayalpha. I share your sentiment completely.